Long Term Evolution (LTE) telecommunication systems are an evolution of Wideband Code Division Multiple Access (WCDMA) telecommunication systems introducing a new air interface. LTE has many attractive properties that can be used for future development of telecommunication services. A specific technical challenge in, e.g., LTE and similar systems is the scheduling of uplink channels to time intervals and frequencies where the interference conditions are favourable, and where there exist a sufficient capacity in the uplink. This can be done since different users in LTE are allocated to different sub-bands (also called tones) during each timeslot. Due to leakage between the sub-bands other existing users of the cell all contribute to the interference level of a specific user in the uplink of LTE systems. Further, terminals in neighbour cells also contribute to the same interference level. This is because all users and common channels of all cells transmit in the same uplink frequency band when LTE technology is used. Thus, users of neighbour cells that transmit on the same tones as users in the own cell will produce interference. Two sources of interference are present—from users in the own cell and from users of neighbour cells.
In order to schedule the traffic in the own and neighbour cells efficiently, it is desirable to know the level of interference for each tone of the uplink. With such knowledge it becomes possible to schedule traffic to free tones where the interference level is low. In that way the transmission from the terminal (UE) to the base station (eNodeB) will be efficient. Reversing the argumentation, it is clear that scheduling to tones with a high interference level should be avoided, because such scheduling interferes with ongoing uplink transmission in neighbour cells.
As discussed above, the interference power at a specific tone is the sum of the interference from neighbour cells and the leakage power from the other tones of the own cell. Now, the leakage from other tones of the own cell depends in a known way on the selected filter bank. Hence, knowledge of the total power levels of the received signals of the uplink of the own cell can be used to compute the expected leakage power, that affects a specific tone. Consequently, it is possible to filter out, at least to some extent, the own cell interference. This leaves the neighbour cell interference as the major source of interference for each tone of the own cell.
The interference level of a specific tone of a cell in, e.g., an LTE system is usually expressed with respect to some reference, typically the thermal noise power floor. It is thus necessary to determine the noise power floor in order to determine the interference level. Determinations of noise floor have in the past typically been associated with relatively large uncertainties, often of a size of several dBs. This is an effect of unknown scale factor errors of the front end receiver electronics. Prior art solutions for estimation of the noise floor, e.g. the international PCT-applications WO 2007/024166 and WO 2008/004924, describe means for noise floor estimation that are suitable for code division multiple access communications systems. They do, however, not disclose any means suitable for estimation of the noise floor for single tones of the LTE uplink. Neither do they address LTE-specific problems, e.g. relating to the filtering of leakage between tones of the own cell, which is a consequence of the uplink multiple access method used in LTE and different from the one used in code division multiple access systems. Finally, they do not address the estimation of the neighbour interference level of specific tones of the LTE uplink, exploiting a (possibly uncertain) estimate of the thermal noise power floor of said specific tones, Therefore, there is a need for methods and arrangements for providing efficient and accurate real time estimates of the thermal noise power floor and the neighbour cell interference level, applicable to the LTE uplink multiple access method.
The admission of new users into the LTE telecommunication system provides a way to regulate the load of LTE cells and may be performed either in the eNodeBs or in another node. The admission rules may typically use information on the total power level of the cell, the own channel power of the cell, the neighbour cell interference level of the cell, as well as information on the thermal noise power floor of the cell. Therefore there is a need for methods and arrangements for aggregating, for each of the subsets of frequency sub-bands of the total LTE frequency band, the total power, own channel power, and neighbour cell interference power to obtain the total cell power, the total own cell channel power, and the total neighbour cell interference level. Furthermore, there is a need for means providing signaling of a subset of the total cell power, the total own cell channel power, the total neighbour cell interference level, and the thermal noise floor measure to an external node, or another function within the e Node B.
Also, the memory consumption associated with the estimation of the thermal noise power flow in an LTE-system may in previously known systems require a too high amount of memory, e.g. about 10-100 MByte of memory, which is not acceptable for an ASIC-implementation.
A general problem with prior art LTE communications networks is that neighbour cell interference estimations are presented with an accuracy that makes careful scheduling of uplink traffic difficult. In particular, the determination of neighbour cell interference suffers from significant uncertainties, primarily caused by difficulties to estimate the noise floor.